Plasma Processing Apparatus

ABSTRACT

A plasma processing apparatus includes a stage which is a lower electrode, an upper electrode which is a counter electrode for the lower electrode, and a processing chamber in which the lower and the upper electrodes are placed. The apparatus supplies a gas to a plasma generation space located between the lower and the upper electrodes to generate a plasma so that a processing object is subjected to plasma processing. In the apparatus, the upper electrode is formed up of a body portion having a gas supply port, a gas-permeable porous plate located on the underside of the body portion so as to close the gas supply port, and a support member for supporting the outer edge portion of the porous plate. Slits for absorption of strain due to thermal expansion in the plasma processing are formed at a pitch in the outer edge portion of the porous plate.

TECHNICAL FIELD

The present invention relates to a plasma processing apparatus for performing plasma processing to a processing object such as a wafer or the like.

BACKGROUND ART

As apparatuses for performing surface treatment of processing objects such as wafers or the like, there have been known plasma processing apparatuses. A plasma processing apparatus operates to produce plasma under a reduced-pressure atmosphere to allow a surface of a processing object to be subjected to etching processing or the like by physical and chemical actions of the plasma. Plasma is generated by applying a high-frequency voltage to an upper electrode or lower electrode while the internal pressure within a sealed processing chamber of the plasma processing apparatus is reduced to a specified pressure with a plasma-generation gas (hereinafter, referred to simply as ‘gas’) fed thereto.

For such plasma processing, it is desirable in some cases to generate high-density plasma depending on the aim of processing. For example, in plasma etching targeted for silicon substrates such as wafers or the like, a process of uniformly spraying and feeding a relatively high-pressure gas to a surface of a silicon wafer is used with a view to improving the processing efficiency.

Known parallel-plate electrode members suited for such plasma processing formed of a gas-permeable porous plate which is a sintered body of ceramic particles (see, e.g., Japanese unexamined patent publication No. 2002-231638 A, JP 2003-7682 A and JP 2003-282462 A). With the use of such a porous plate, it becomes possible to uniformly generate high-density plasma so that a stable plasma processing is carried out with high etching efficiency.

DISCLOSURE OF INVENTION

With a processing object set on a stage which is the lower electrode within the processing chamber, as plasma processing is started by applying a high-frequency voltage to the upper electrode or lower electrode, the porous plate provided on one side closer to the upper electrode, which is a counter electrode to the lower electrode, rapidly increases in temperature. Whereas the porous plate typically has a diameter of about 220 mm or 320 mm and a thickness of about 2 to 10 mm, the porous plate does not increase in temperature uniformly as a whole, but does increase in temperature first rapidly in vicinities of a central portion of a counter surface (normally, lower surface) confronting the lower electrode (typically, rapidly increases from normal temperature to approximately 200° C. for about 30 seconds), and then increases in temperature gently at an outer edge portion of the porous plate more slowly than in the vicinities of the central portion. As a result, strain due to nonuniform temperature increases occurs to the porous plate, so that cracks might occur at the outer edge portion of the porous plate (for example, radial cracks occur to outer peripheral edge portions because the porous plate is generally a disc-shaped). This might cause the porous plate to be fractured and thus damaged, disadvantageously.

Accordingly, an object of the present invention, lying in solving the above problem, is to provide a plasma processing apparatus in which damage due to occurrence of cracks in an outer edge portion of a porous plate caused by thermal expansion due to rapid temperature increases in plasma processing can be prevented, thus allowing a stable plasma processing to be carried out.

According to a first aspect of the present invention, there is provided a plasma processing apparatus comprising a first electrode unit having a placement surface on which a processing object is to be placed, and a second electrode unit facing the placement surface of the first electrode unit, and a processing vessel that defines a processing chamber in which the first and second electrode units are to be located, wherein a plasma-generation gas is supplied into a plasma processing space between the first and second electrode units so as to generate a plasma and then plasma processing on the processing object is performed,

the second electrode unit comprising:

-   -   a body portion having a gas supply port communicating with a gas         supply passage;     -   a porous plate which is placed so as to cover the gas supply         port and face the plasma processing space and which has gas         permeability such that the gas supplied from the gas supply port         is supplied to the plasma processing space through inside         thereof; and     -   a support member which supports the porous plate on its outer         edge portion so that the porous plate is fixedly placed to the         body portion, wherein

a plurality of cutout portions are formed in the outer edge portion of the porous plate at a specified interval pitch so as to extend through the plate in a thicknesswise direction thereof.

According to a second aspect of the present invention, there is provided the plasma processing apparatus as defined in the first aspect, wherein

the porous plate has a disc-like shape,

the support member includes an annular member located on a lower surface of the body portion, and a protruding portion annularly protruded inward of an end portion of the annular member, and

the outer edge portion of the porous plate located inward of the annular member in the lower surface of the body portion is supported by the protruding portion from below.

According to a third aspect of the present invention, there is provided the plasma processing apparatus as defined in the second aspect, wherein the protruding portion is formed so as to project over the individual cutout portions so that gaps of the individual cutout portions of the porous plate are closed against the plasma processing space.

According to a fourth aspect of the present invention, there is provided the plasma processing apparatus as defined in the third aspect, wherein

the porous plate has a support region which is an annular region located in an outer edge portion of the disc-like shape and on which the plate is supported by the protruding portion of the support member, and a gas passage region which is a circular region located inside the outer edge portion of the disc-like shape and surrounded by the support region and in which the plasma-generation gas is allowed to pass therethrough, and

each of the cutout portions is formed in the support region so as to be in close proximity to a boundary with the gas passage region.

According to a fifth aspect of the present invention, there is provided the plasma processing apparatus as defined in the fourth aspect, wherein in each of the cutout portions of the porous plate, at least an inner circumferential surface on one side closer to a center of the porous plate is formed into a curved surface.

According to a sixth aspect of the present invention, there is provided the plasma processing apparatus as defined in the fifth aspect, wherein in the protruding portion, each of the cutout portions is so formed that an entirety of its inner circumferential surface becomes a curved surface.

According to a seventh aspect of the present invention, there is provided the plasma processing. apparatus as defined in the first aspect, wherein each of the cutout portions has a slit-like shape.

According to the present invention, when plasma processing is started, the porous plate increases in temperature rapidly first in vicinities of its central portion, causing large temperature differences between its outer edge portion and vicinities of the central portion, so that strain due to temperature increases occurs, in particular, to the outer edge portion. Since such occurred strain can be absorbed by respective cutouts portions provided at the outer edge portion, the porous plate can be prevented from being damaged due to occurrence of cracks at the outer edge portion of the plate or other reasons. Further, the individual cutout portions of the porous plate are closed against the plasma processing space by support member, thereby it becomes possible to prevent a gas leakage through the cutout portions and to uniformly generate plasma in the whole plasma processing space.

BRIEF DESCRIPTION OF DRAWINGS

These and other aspects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which:

FIG. 1 is a sectional view of a plasma processing apparatus according to an embodiment of the present invention;

FIG. 2 is a perspective view of a porous plate of the embodiment;

FIG. 3 is a perspective view (including a partly cut-out cross section) of a support member in which the porous plate is housed in the embodiment;

FIG. 4 is a partly enlarged sectional view of an upper electrode portion in the embodiment;

FIG. 5A is a schematic plan view of a conventional porous plate;

FIG. 5B is a schematic sectional view taken along the line A-A in the conventional porous plate of FIG. 5A;

FIG. 6A is a schematic plan view of the porous plate according to the embodiment of the present invention;

FIG. 6B is a schematic sectional view taken along the line B-B in the porous plate of FIG. 6A;

FIG. 7 is a partial schematic plan view showing a configuration of a slit of a porous plate according to a modification example of the embodiment of the present invention;

FIG. 8 is a schematic explanatory view for explaining the formation method for the slit of FIG. 7;

FIG. 9 is a partial schematic plan view showing a configuration of a cutout portion of a porous plate according to another modification example of the embodiment of the present invention;

FIG. 10 is a schematic explanatory view for explaining the formation method for the cutout portion of FIG. 9.

BEST MODE FOR CARRYING OUT THE INVENTION

Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings.

Hereinbelow, one embodiment of the present invention is described in detail with reference to the accompanying drawings.

First, a plasma processing apparatus according to this embodiment is explained with reference to FIG. 1. Referring to FIG. 1, a vacuum chamber (or a vacuum vessel) 1, which is an example of a processing vessel, internally has a processing chamber 2 for performing plasma processing, and a lower electrode 3 which is an example of a first electrode unit and an upper electrode 4 which is an example of a second electrode unit are placed in up-and-down opposition to each other inside the processing chamber 2, by which a parallel-plate type plasma processing apparatus is made up.

The lower electrode 3, which includes a stage 31 serving as a high-frequency electrode and a protruding portion 32 that protrudes downward from a central portion of the stage 31, is fitted inside the vacuum chamber 1 via an insulating member 33 provided around the outer edge portion of the stage 31. A high-frequency power supply unit 5 is electrically connected to the protruding portion 32 of the lower electrode 3. An exhaust passage 6 is formed at a side portion of the insulating member 33, serving for vacuum suction of the interior of the processing chamber 2 by an exhaust unit 7 such as a vacuum pump. On the stage 31, a processing object W such as a wafer is to be mounted.

The upper electrode 4, which is the counter electrode, includes a flat plate (disc-like plate)-shaped body portion 41, an annular support member 45 provided around a lower-surface outer peripheral portion of the body portion 41, and a porous plate 43 housed inside the support member 45 below the body portion 41. The upper electrode 4 is fitted to the vacuum chamber 1 via a protruding portion 42 that protrudes upward from a central portion of the body portion 41.

The porous plate 43 is a ceramic porous plate formed into a disc-like shape from a porous material which is formed from a sintered body of ceramic particles and which has gas permeability. More specifically, the porous plate 43, i.e. ceramic porous plate, has a three-dimensional mesh-like structure having ceramic skeletal portions formed continuously into a three-dimensional mesh and having a multiplicity of void portions (gaps) inside. Then, the individual void portions of this three-dimensional mesh-like structure are communicated with one another, and a multiplicity of irregular passages are formed so as to allow gas fed to one surface of the porous plate 43 to pass to the other surface.

The support member 45 has such an annular shape so as to allow the porous plate 43 to be placed inside thereof and supported. Further, the support member 45 is further provided with a protruding portion (or annular support end portion) 45′ that annularly protrudes inward (toward the central portion) from its inner wall lower portion. The porous plate 43 is housed in an internal space defined by the body portion 41 and the support member 45 with the outer edge portion (outer peripheral edge portion because the porous plate 43 of this embodiment is disc-like-shaped) entirely rested on the protruding portion 45′.

In FIGS. 2 and 3, the porous plate 43 provided on the upper electrode 4 side is disc-like-shaped, and slits S, which are an example of cutout portions, are formed at specified intervals on its outer peripheral edge portion so as to extend thicknesswise (vertically) through the porous plate 43 with the radial direction of the porous plate 43 aligned with the longitudinal direction of the slits S. For example, in the case where the porous plate 43 has a diameter of about 220 mm or 320 mm, each slit S desirably has a length L1 of about 3 to 10 mm as well as a width L2 of about 0.5 mm to 1.0 mm, and moreover, desirably, the slits S are formed at an interval pitch L3 of 120 mm or less. It is noted that such a cutout portion can also be said to be a recess portion, as the porous plate 43 is seen along its radial direction.

FIG. 4 shows a desirable connecting structure among the body portion 41, the support member 45 and the porous plate 43. The support member 45 is coupled to the body portion 41 by fittings such as bolts 10 or nuts 11. An upper surface “a” of the protruding portion 45′ is a inwardly descending sloped tapered surface, and a lower surface “b” of the outer peripheral edge portion of the porous plate 43 is an outwardly ascending tapered surface, where the upper surface “a” and the lower surface “b” are joined together in close contact so as not to form any gap. Also, the protruding portion 45′ extends inward (toward the central portion) more than the slits S, so that the slits S are closed at lower side thereof by the protruding portion 45′. As a result of this, a gas supply port T (described later) on the lower side of the body portion 41 is kept hermetic, so that a gas supplied to the gas supply port T is prevented from leaking to a plasma generation space A through the slits S. In addition, by the arrangement that the outer peripheral edge portion of the porous plate 43 and the protruding portion 45′ of the support member 45 each have a tapered surface, the lower surface of the porous plate 43 and the lower surface of the support member 45 can be made generally flush with each other in height position in the state that the porous plate 43 is supported by the protruding portion 45′, so that the discharge stability in plasma processing can be improved, compared with cases where no tapered surfaces are provided.

The upper surface of the porous plate 43 near the outer peripheral edge portion is an outwardly descending tapered surface “c”, and a cushioning member 12 is provided between the tapered surface “c” and a portion of the body portion 41 near the outer peripheral edge portion of the porous plate 43. The cushioning member 12, which is made from an elastic material such as resin rubber, is ring-shaped as viewed in plan view, ensuring the hermeticity of the gas supply port (or a space for supplying the gas) T, which is a narrow gas flow space between the cushioning member 12 and a portion of the porous plate 43 on the lower surface side of the body portion 41.

In FIG. 1, in the body portion 41 and the protruding portion 42, a gas supply passage 46 is formed so as to vertically extend through those members. The body portion 41 is electrically grounded to a ground portion 44. The gas at the gas supply portion 13 is supplied through the gas supply passage 46 to the gas supply port T, passing inside the porous plate 43, so as to be supplied to the plasma generation space (plasma processing space) A between the lower electrode 3 and the upper electrode 4. Although the upper electrode 4 is electrically grounded in this embodiment, it is also possible that the lower electrode 3 is grounded while the upper electrode 4 is electrically connected to the high-frequency power supply.

This plasma processing apparatus having a structure described above, its operation is now explained. In a state that a processing object W such as a wafer is mounted on the stage 31, the exhaust unit 7 is activated to reduce the internal pressure of the processing chamber 2. Now that the interior of the processing chamber 2 has been reduced to a specified pressure, the gas is supplied from the gas supply portion 13 to the gas supply port T and let to pass through within the porous plate 43 so as to be fed out to the plasma generation space A between the two electrodes 3, 4. In this state, as a high-frequency voltage is applied to the lower electrode 3, plasma is generated in the plasma generation space A, where the processing object W is subjected to surface treatment such as plasma etching processing.

As the plasma processing is started as described above, the plasma generation space A rapidly increases in temperature, so that the porous plate 43 increases in temperature first rapidly in vicinities of the central portion of the counter surface (lower surface) of the porous plate 43 confronting the lower electrode 3. Because of thermal expansion due to this temperature increase, there occurs strain to the porous plate 43 especially at its outer peripheral edge portion. However, since the strain is absorbed by the slits S, no cracks, which may cause gas leakage, occur to the outer peripheral edge portion, so that a uniform, stable plasma processing is carried out.

Now the principle of absorption of strain due to thermal expansion by the porous plate 43 of this embodiment is concretely explained with reference to the accompanying drawings. In conjunction with this explanation, a schematic plan view of a conventional porous plate 543 having a structure that no cutout portions such as slits are formed is shown in FIG. 5A, and a schematic sectional view taken along the line A-A in the conventional porous plate 543 of FIG. 5A is shown in FIG. 5B. Also, a schematic plan view of the porous plate 43 with the slits S formed therein according to this embodiment of the present invention is shown in FIG. 6A, and a schematic sectional view taken along the line B-B in the porous plate 43 of FIG. 6A is shown in FIG. 6B.

First, as shown in FIGS. 5A and 5B, the porous plate 543 having a disc-like shape is supported at the entire lower surface of its annular outer peripheral edge portion by a protruding portion 545′ of a support member 545, where the supported portion serves as a support region R1, which is an annular region (or an planar annular region), with which the lower surface of the porous plate 543 is covered without being exposed to the plasma generation space A. Meanwhile, inside this outer peripheral edge portion, the lower surface of the porous plate 543 is exposed to the plasma generation space A and serves as a gas passage region R2 that allows the plasma-generation use gas supplied to the gas supply port T to pass through within the porous plate 543 so as to be supplied to the plasma generation space A.

After the state of the plasma processing, with the plasma generation space A rapidly increased in temperature, first in the porous plate 543, its portion corresponding to the gas passage region R2 is rapidly increased in temperature. Meanwhile, the support region R1, which is a region surrounding the gas passage region R2 and which is covered with the protruding portion 545′ without being exposed to the plasma generation space A, is more gently increased in temperature, compared with the gas passage region R2. Therefore, the portion corresponding to the gas passage region R2 becomes high in temperature while the portion corresponding to the support region R1 becomes relatively low in temperature, so that a large temperature difference (e.g., about 50° C.) occurs therebetween, resulting in a difference in the amount of thermal expansion. As a result of this, as shown in FIGS. 5A and 5B, radial stresses F1 directed from the gas passage region R2 of the porous plate 543 toward its surrounding support region R1 occur radially. Particularly in the support region R1, the stresses become a maximum at its outer peripheral end portion, causing resultant stresses F2 to occur along the circumferentially. In such a situation, at the outer peripheral edge portion of the porous plate 543, cracks or the like are liable to occur due to the stresses F2 acting circumferentially.

On the other hand, in the porous plate 43 of this embodiment shown in FIGS. 6A and 6B, in which a plurality of slits S are formed in the support region R1, even if radial stresses F1 act in the gas passage region R2 similarly, stresses (tensile stress) F3 occurring at the outer peripheral end portion of the support region R1 can be divided by intervals between the individual slits S, respectively, so that the stresses F3 can be reduced in magnitude thereof. That is, at the individual slits S, which are subjected to minute elastic deformation so as to be expanded in their gap distances, it becomes achievable to reduce the magnitude of the stresses F3.

For more effective obtainment of such a thermal expansion absorption function of the slits S, it is preferable that end portions of the slits S are positioned in the support region R1 so as to be in close proximity to its boundary with the gas passage region R2, i.e., the slits S are formed in the support region R1 so that the radial cut-in depth of the slits S becomes more deeper. By such formation of the slits S, the amount of elastic deformation attributed to their shape can be increased, and the suppression effect for the stresses caused by thermal expansion can be further improved.

The embodiment shown above has been described on a case where the slits S are formed as an example of the cutout portions in the porous plate 43. However, other various modification examples may be applied.

For instance, as shown in FIG. 7, which is a partly enlarged schematic plan view of an outer peripheral edge portion of a porous plate 143 of FIG. 7, roughly U-shaped slits S′ may be formed. In the case of such a U-shaped slit S′, since a central side inner circumferential surface of the porous plate 143 is formed of a curved surface, an effect of suppressing stress concentration can be obtained, so that occurrence of cracks or the like to the inner circumferential surface of the slit S′ can be prevented. Such a slit S′ can be formed by, for example, cutting process with the use of a disc-shaped cutting tool 150 having an outer peripheral end portion formed of a curved surface, as shown in the schematic explanatory view of FIG. 8. It is noted that the curved surface to be formed in such a slit S′ is preferably formed into a gently curved surface from the viewpoint of suppressing stress concentration.

Accordingly, for instance, a generally semicircular-shaped cutout portion C having an inner circumferential surface formed of a curved surface alone may be formed as shown in FIG. 9, which is a partly enlarged schematic plan view of an outer peripheral edge portion of a porous plate 243. This cutout portion C, although having a cut-in depth Al in the radial direction of the porous plate equal to the cut-in depth Al of the slit S′ of FIG. 7, yet has an opening size B2, which is the circumferential width, formed larger than an opening size B1 of the slit S′ because of the circumferential surface formed entirely of a curved surface. By the arrangement that the inner circumferential surface of the cutout portion C is formed of a curved surface alone (or formed of a curved surface in most part), it becomes possible to disperse the stresses to more extent, so that occurrence of cracks or the like can be prevented more reliably. It is noted that such cutout portions C can be formed by, for example, cutting process with the use of a bar-shaped cutting tool 250 having a circular-shaped cross section as shown in a schematic explanatory view of FIG. 10.

In the above-described individual aspects of this embodiment, the individual cutout portions (including slits) are preferably made identical in configuration and size and, besides, arranged at an equidistant pitch in order to more uniformly relax stresses that occurs at the outer peripheral edge portion of the porous plate.

However, from the viewpoints of the capacity occupied by the cutout portions and the strength sustainment for the porous plate, relatively large cutout portions and small cutout portions may be formed compositely in the outer peripheral edge portion of the porous plate (that is, mixed-arrangement of the large and small cutout portions may be applied). In such a case, it is preferable, from the viewpoint of the uniformity of stress relaxation, that the arrangement of the individual cutout portions is made symmetrical.

Also, in the above embodiment, other members may be arranged within the individual cutout portions of the porous plate unless elastic deformation of the cutout portions serving for the absorption of any strain due to thermal expansion is inhibited. Further, the inner circumferential surfaces of the cutout portions may be subjected to surface finishing or the like in order to suppress gas passage. With such an arrangement, the gas passage through the inner circumferential surfaces of the cutout portions in the porous plate may be suppressed.

According to the present invention, although strain occurs to the outer edge portion of the porous plate because of thermal expansion due to rapid temperature increases in the plasma processing, yet the strain is absorbed by the cutout portions, so that the porous plate can be prevented from being damaged due to occurrence of cracks at the outer edge portion or the like. Therefore, a stable plasma processing can be carried out, and the plasma processing apparatus including such a porous plate is useful as those of plasma processing apparatuses for use of, in particular, surface etching of wafer or the like.

It is to be noted that, by properly combining the arbitrary embodiments of the aforementioned various embodiments, the effects possessed by them can be produced.

Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.

The disclosure of Japanese Patent Application No.2005-108385 filed on Apr. 5, 2005 including specification, drawing and claims are incorporated herein by reference in its entirety. 

1. A plasma processing apparatus comprising a first electrode unit having a placement surface on which a processing object is to be placed, and a second electrode unit facing the placement surface of the first electrode unit, and a processing vessel that defines a processing chamber in which the first and second electrode units are to be located, wherein a plasma-generation gas is supplied into a plasma processing space between the first and second electrode units so as to generate a plasma and then plasma processing on the processing object is performed, the second electrode unit comprising: a body portion having a gas supply port communicating with a gas supply passage; a porous plate which is placed so as to cover the gas supply port and face the plasma processing space and which has gas permeability such that the gas supplied from the gas supply port is supplied to the plasma processing space through inside thereof; and a support member which supports the porous plate on its outer edge portion so that the porous plate is fixedly placed to the body portion, wherein a plurality of cutout portions are formed in the outer edge portion of the porous plate at a specified interval pitch so as to extend through the plate in a thicknesswise direction thereof.
 2. The plasma processing apparatus as defined in claim 1, wherein the porous plate has a disc-like shape, the support member includes an annular member located on a lower surface of the body portion, and a protruding portion annularly protruded inward of an end portion of the annular member, and the outer edge portion of the porous plate located inward of the annular member in the lower surface of the body portion is supported by the protruding portion from below.
 3. The plasma processing apparatus as defined in claim 2, wherein the protruding portion is formed so as to project over the individual cutout portions so that gaps of the individual cutout portions of the porous plate are closed against the plasma processing space.
 4. The plasma processing apparatus as defined in claim 3, wherein the porous plate has a support region which is an annular region located in an outer edge portion of the disc-like shape and on which the plate is supported by the protruding portion of the support member, and a gas passage region which is a circular region located inside the outer edge portion of the disc-like shape and surrounded by the support region and in which the plasma-generation gas is allowed to pass therethrough, and each of the cutout portions is formed in the support region so as to be in close proximity to a boundary with the gas passage region.
 5. The plasma processing apparatus as defined in claim 4, wherein in each of the cutout portions of the porous plate, at least an inner circumferential surface on one side closer to a center of the porous plate is formed into a curved surface.
 6. The plasma processing apparatus as defined in claim 5, wherein in the protruding portion, each of the cutout portions is so formed that an entirety of its inner circumferential surface becomes a curved surface.
 7. The plasma processing apparatus as defined in claim 1, wherein each of the cutout portions has a slit-like shape. 